Synthesis of Dihydrooxepin Models Related to the Antitumor Antibiotic MPC1001

Progress in the Stereoselective Synthesis Methods of Pyrrolidine-Containing Drugs and Their Precursors

The presented review systematizes and summarizes the data on the synthesis of pyrrolidine derivatives, which are precursors for obtaining drugs. Based on the analysis of published data, the most promising directions in the synthesis of biologically active compounds containing a pyrrolidine ring are identified. Stereoselective synthesis methods are classified based on the source of the pyrrolidine ring. The first group includes methods that use a pyrrolidine ring as the starting compound. The second group combines stereoselective methods of cyclization of acyclic starting compounds, which lead to optically pure pyrrolidine derivatives.

Asperemestrins A-D, Emestrin Hybrid Polymers with Bridged Skeletons from the Endophytic Fungus Aspergillus nidulans

Four emestrin hybrid polymers, asperemestrins A-D (1-4, respectively), were isolated from the fungus Aspergillus nidulans. Asperemestrins A-C are the first examples of emestrin-sterigmatocystin heterodimers bearing a 7/5/6/6/5/5/6/6/6 nonacyclic system with a 2,5-diazabicyclo[2.2.2]octane-3,6-dione core, while asperemestrin D features an unprecedented 2,15-dithia-17,19-diazabicyclo[14.2.2]icosa-4,8-diene-12,18,20-trione core skeleton. Their structures were determined by extensive spectroscopic data, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Asperemestrin B showed moderate cytotoxicity against cancer cell lines, including SU-DHL-2, HEPG2, and HL-60.

Formation of Enol Ethers by Radical Decarboxylation of α-Alkoxy β-Phenylthio Acids

Enol ethers are formed by radical decarboxylation of α-alkoxy β-phenylthio acids via the corresponding Barton esters. The phenylthio acids were usually made by the known regioselective reaction of α,β-epoxy acids with PhSH in the presence of InCl₃, followed by O-alkylation of the resulting alcohol. In one case, thiol addition to an α,β-unsaturated ethoxymethyl ester was used.

The Oxepane Motif in Marine Drugs

Oceans have shown to be a remarkable source of natural products. The biological properties of many of these compounds have helped to produce great advances in medicinal chemistry. Within them, marine natural products containing an oxepanyl ring are present in a great variety of algae, sponges, fungus and corals and show very important biological activities, many of them possessing remarkable cytotoxic properties against a wide range of cancer cell lines. Their rich chemical structures have attracted the attention of many researchers who have reported interesting synthetic approaches to these targets. This review covers the most prominent examples of these types of compounds, focusing the discussion on the isolation, structure determination, medicinal properties and total synthesis of these products.

Enantioselective Synthesis of (-)-Acetylapoaranotin

The first enantioselective total synthesis of the epipolythiodiketopiperazine (ETP) natural product (-)-acetylapoaranotin (3) is reported. The concise synthesis was enabled by an eight-step synthesis of a key cyclohexadienol-containing amino ester building block. The absolute stereochemistry of both amino ester building blocks used in the synthesis is set through catalytic asymmetric (1,3)-dipolar cycloaddition reactions. The formal syntheses of (-)-emethallicin E and (-)-haemotocin are also achieved through the preparation of a symmetric cyclohexadienol-containing diketopiperazine.

Emestrins: Anti-Cryptococcus Epipolythiodioxopiperazines from Podospora australis

Eleven emestrin-type epipolythiodioxopiperazines, including four new compounds, emestrins H-K (1-4), were isolated from the crude extracts of two strains of the coprophilous fungus Podospora australis. The structures of 1-4 were established primarily by analysis of NMR data, and the absolute configuration of C-6 in 1 was independently assigned using the modified Mosher method. Four of the known emestrins obtained (emestrins C-E and MPC1001C) were found to selectively inhibit the growth of Cryptococcus neoformans. These results also represent the first report of chemistry from any strain of P. australis.

Synthesis of models of the BC ring systems of MPC1001 and MPC1001F

Piperazinedione and piperazinetrione systems representing the BC rings of several members of the MPC1001 family of fungal metabolites were synthesized.

General synthetic approach to functionalized dihydrooxepines

A three-step sequence to access functionalized 4,5-dihydrooxepines from cyclohexenones has been developed. This approach features a regioselective Baeyer-Villiger oxidation and subsequent functionalization via the corresponding enol phosphate intermediate.

SYNTHETIC STUDIES ON MPC1001: A DIPOLAR CYCLOADDITION APPROACH TO THE PYRROLIDINE RING SYSTEM

A novel [1,3]-dipolar azomethine ylide cycloaddition has been developed in an approach to the synthesis of the MPC1001 family of natural products.

A unified strategy targeting the thiodiketopiperazine mycotoxins exserohilone, gliotoxin, the epicoccins, the epicorazines, rostratin A and aranotin

A unified synthetic strategy directed towards mycotoxins belonging to the thiodiketopiperazine family is reported. The building blocks for a number of natural products--including exserohilone, gliotoxin, the epicoccins, the epicorazines, rostratin A and aranotin--have been synthesised stereoselectively from a common precursor. This key intermediate was constructed through an efficient and highly diastereoselective [2+2] cycloaddition between a ketene and an enecarbamate derived from L-pyroglutamic acid. The annelation of the second ring was accomplished through ring-closing metathesis and enol ether-olefin ring-closing metathesis to provide both cis- and trans-annelated azabicyclic cyclohexenones, as well as an annelated seven-membered cyclic enol ether. A Pd-catalysed elimination of allyl acetate gave rise to the cyclohexadienol structure of gliotoxin. Dimerisation of one building block to afford the diketopiperazine core was demonstrated.

Macrocyclization by nickel-catalyzed, ester-promoted, epoxide-alkyne reductive coupling: total synthesis of (-)-gloeosporone

Ringing the changes: The total synthesis of the title compound centers around a novel strategy that employs a nickel(0)-phosphine complex and triethyl borane in an efficient closure of a 14-membered ring through C--C bond formation (see scheme; cod=cyclooctadiene). The synthesis was accomplished in 10 steps and in approximately 9 % overall yield.